Synthesis of (-)-Monanchoradin A and (-)-Crambescin A2 392 Based on a Cyclization-Carbonylation-Cyclization Cascade

Syntheses of guanidino alkaloids (-)-monanchoradin A and (-)-crambescin A2 392 are described. The key feature of the syntheses is the cyclization-carbonylation-cyclization cascade of the optically active propargyl guanidine. The bicyclic guanidino cores bearing an asymmetric center and ester or carboxylic acid functionality were constructed in a single step. The carboxylic acid was then converted to (-)-monanchoradin A and (-)-crambescin A2 392.

Inhibition of veratridine-induced delayed inactivation of the voltage-sensitive sodium channel by synthetic analogs of crambescin B

Crambescin B carboxylic acid, a synthetic analog of crambescin B, was recently found to inhibit the voltage-sensitive sodium channels (VSSC) in a cell-based assay using neuroblastoma Neuro 2A cells. In the present study, whole-cell patch-clamp recordings were conducted with three heterologously expressed VSSC subtypes, Na_v1.2, Na_v1.6 and Na_v1.7, in a human embryonic kidney cell line HEK293T to further characterize the inhibition of VSSC by crambescin B carboxylic acid. Contrary to the previous observation, crambescin B carboxylic acid did not inhibit peak current evoked by depolarization from the holding potential of -100mV to the test potential of -10mV in the absence or presence of veratridine (VTD). In the presence of VTD, however, crambescin B carboxylic acid diminished VTD-induced sustained and tail currents through the three VSSC subtypes in a dose-dependent manner, whereas TTX inhibited both the peak current and the VTD-induced sustained and tail currents through all subtypes of VSSC tested. We thus concluded that crambescin B carboxylic acid does not block VSSC in a similar manner to TTX but modulate the action of VTD, thereby causing an apparent block of VSSC in the cell-based assay.

The chemistry and biology of guanidine natural products

The chemistry and biology of natural guanidines isolated from microbial culture media, from marine invertebrates, as well as from terrestrial plants and animals, are reviewed.

A Synthetic Strategy for Saxitoxin Skeleton by a Cascade Bromocyclization: Total Synthesis of (+)-Decarbamoyl-α-saxitoxinol

A new synthetic strategy for the formation of the ABC tricyclic framework of saxitoxin was developed. The BC ring moiety, including a spiro-aminal structure, was first constructed stereoselectively by a newly designed cascade bromocyclization of a readily available internal alkyne bearing guanidine and urea. The A ring was then synthesized by a guanylation of a cyclic urea, easily prepared via the oxidative cleavage of the diol of the cascade product, followed by addition of cyanide. This strategy enables the concise stereocontrolled total synthesis of (+)-decarbamoyl-α-saxitoxinol, which is a naturally occurring saxitoxin analogue.

Asymmetric synthesis of crambescin A–C carboxylic acids and their inhibitory activity on voltage-gated sodium channels

Both enantiomers of crambescin A–C carboxylic acids were synthesized via Katsuki asymmetric epoxidation and bromocation-triggered cascade cyclization.

The chemistry and biology of guanidine natural products

The present review discusses the isolation, structure determination, synthesis, biosynthesis and biological activities of secondary metabolites bearing a guanidine group.

Anti-parasitic Guanidine and Pyrimidine Alkaloids from the Marine Sponge Monanchora arbuscula

HPLC-UV-ELSD-MS-guided fractionation of the anti-parasitic extract obtained from the marine sponge Monanchora arbuscula, collected off the southeastern coast of Brazil, led to the isolation of a series of guanidine and pyrimidine alkaloids. The pyrimidines monalidine A (1) and arbusculidine A (7), as well as the guanidine alkaloids batzellamide A (8) and hemibatzelladines 9-11, represent new minor constituents that were identified by analysis of spectroscopic data. The total synthesis of monalidine A confirmed its structure. Arbusculidine A (7), related to the ptilocaulin/mirabilin/netamine family of tricyclic guanidine alkaloids, is the first in this family to possess a benzene ring. Batzellamide A (8) and hemibatzelladines 9-11 represent new carbon skeletons that are related to the batzelladines. Evaluation of the anti-parasitic activity of the major known metabolites, batzelladines D (12), F (13), L (14), and nor-L (15), as well as of synthetic monalidine A (1), against Trypanosoma cruzi and Leishmania infantum is also reported, along with a detailed investigation of parasite cell-death pathways promoted by batzelladine L (14) and norbatzelladine L (15).

Syntheses of Cyclic Guanidine-Containing Natural Products

Naturally occurring guanidine derivatives frequently display medicinally useful properties. Among them, the higher order pyrrole-imidazole alkaloids, the dragmacidins, the crambescidins/batzelladines, and the saxitoxins/tetradotoxins have stimulated the development of many new synthetic methods over the past decades. We provide here an overview of the syntheses of these cyclic guanidine-containing natural products.